This invention relates to integrated circuits and, more specifically, to capacitor structures in integrated circuits and a method for making them.
Capacitors are used extensively in electronic devices for storing an electric charge. The capacitors essentially comprise two conductive plates separated by an insulator. The capacitance, or amount of charge held by the capacitor per applied voltage, is measured in farads and depends upon the area of the plates, the distance between them, and the dielectric value of the insulator. Capacitors are used in filters, in analog-to-digital converters (ADCs), in memories, and various control applications. Capacitors in integrated circuits are usually fabricated from polysilicon, metal to polysilicon, or metal to polycide structures.
In addition, in any fabrication process, simplicity is an advantage. Thus, a fabrication method which can achieve the same or better quality product with the same cost of materials while using fewer steps is highly preferred, especially if elimination of fabrication steps reduces labor costs and the need for expensive manufacturing equipment. A new structure built from materials already being used in the fabrication process is preferred since it reduces materials development efforts and the need for expensive manufacturing equipment. Thus, it would be desirable to provide a process to manufacture high quality capacitors in integrated circuits using a simple manufacturing process.
The present invention is directed to a new capacitor and a new method for fabricating the capacitor in an integrated circuit. The method uses fewer steps than those used in prior art processes. In accordance with the invention, trenches of differing depths are formed in a first insulating layer. One of the trenches is etched to expose a conducting layer formed under the insulating layer. Conductive material is deposited in the trenches to form a capacitor. The trenches are formed apart from each other.